1. Field of the Invention
The present invention relates to an image pickup apparatus that has an autofocus function and to an image pickup device.
2. Description of the Related Art
Recently, a number of portable appliances with a photographing capability such as a digital camera (image pickup apparatus) have been equipped with an autofocus function. Some image pickup apparatuses of this type use an image pickup device that incorporates pixels for focus detection (hereinafter referred to as “AF pixel”) in addition to image pickup pixels (normal pixels) for forming images so as to implement a pupil split phase difference method for autofocus. In this approach, a pupil is split into right and left, and AF pixels with image pickup units that separately receive a luminous flux passing through the right or left pupil need to be built into an image pickup device. Autofocus can be faster by performing a computation on an image signal from such a variety of AF pixels (hereinafter referred to as “AF computation” or “correlation computation”) to generate an AF signal for focusing and performing focusing.
To improve autofocusing performance, however, a relatively large number of AF pixels need to be arranged in the image pickup device, and lack of image signal of the AF pixel portions disadvantageously causes degradation of picked-up image quality.
For this reason, Japanese Patent Application Laid-Open Publication No. 2007-155929 proposes a technique for reducing the number of AF pixels by using normal pixels to estimate pixel values for AF pixels.
Some other image pickup devices include microlenses disposed over the respective pixels. The microlenses are eccentric depending on pixel positions in the image pickup device to appropriately direct light from a taking lens to a light receiving area of each pixel. Japanese Patent Application Laid-Open Publication No. 2009-290157, for example, discloses a technique in which the microlenses are eccentric depending on pixel positions and the light receiving area is defined on a line extending through the center of an exit pupil and the vertex of a microlens. This allows a luminous flux passing through a right or left pupil to reliably impinge on a separate right or left AF pixel, and AF accuracy is therefore improved.